Fetomaternal opioid levels and parturition

The present study evaluates the plasma level changes in β-lipotropin and β-endorphin in nine women at term throughout spontaneous labor, in ten pregnant women undergoing elective cesarean section in the absence of uterine contractions, and in ten women submitted to emergency cesarean section because of fetal distress occurring during labor. A basal plasma sample was taken before labor in the 39th week of pregnancy. Two subsequent samples were then obtained before and after parturition, together with umbilical cord samples at birth. β-lipotropin and β-endorphin were measured by radioimmunoassay after silicic acid plasma extraction and gel filtration. In cases of spontaneous labor, there was a progressive increase in opioid concentrations as labor progressed, the maximal values being observed after delivery. Cord values were similar to those observed in the mother, without showing any relationship to them. Pregnant women undergoing cesarean section in the absence of labor show constant β-lipotropin and β-endorphin concentrations both before and after fetal extraction, both values being significantly lower than those found at delivery after spontaneous labor. β-Endorphin neonatal levels were significantly higher than in the respective mothers and were in the same range as those of infants born through vaginal delivery. In the third group (cesarean section performed at the first stage of labor), presurgical opioid levels were higher than in women at the same stage of spontaneous labor, whereas postextraction values showed a wide range, with mean values similar to those observed after spontaneous delivery. β-Endorphin cord concentrations in infants with one-minute Apgar scores less than 7 (five cases) were higher than those found in infants with Apgar scores of 8 to 10. However, this did not influence maternal levels. These data indicate that the raised opioid levels found after vaginal delivery could be entirely ascribed to pain, stress, and probably the emotional state that accompany labor. Opposingly, when other stress factors such as fetal distress are present, the maternal concentrations of β-lipotropin and β-endorphin seem not to increase. Opioid cord concentrations are unrelated to the maternal values and apparently are not affected by the mode of parturition. They seem more closely related to the condition of the fetus. © 1983 by The American college of Obstetricians and Gynecologists.